The literature review indicates that studies on the structures and properties of perovskites materials have shown attractive applications in the fields of energy, catalysts and sensing materials for fuel cell and sensing industries. Kinetic phenomena in thin film systems, such as solid state amorphization and interface reactions due to diffusion during thin film deposition, are introduced indicating that thermal stability is a concern in thin film sensor device application. The principle of traditional methods of materials characterization is briefly discussed. Emphasis is placed on the functions of analytical transmission electron microscopy. / The SrFeO3/SiO2/Si and SrFeO3/Al 2O3 thin film systems have been studied using transmission electron microscopy. The thin films of SrFeO3 were grown by pulsed laser deposition. For the SrFeO3/SiO2/Si system, TEM characterization showed that the microstructure of the film deposited at room temperature contained crystalline and amorphous layers. Silicon diffusion into SrFeO3 films occurred at the SiO2 interface. The silicon-induced interfacial reactions resulted in phase transformations and the growth of complex crystalline and amorphous phases. The principal compositions of these phases were Sr(Fe,Si)12O19, SrOx and amorphous [Sr-Fe-Si-O]. / The films in the SrFeO3/Al2O3 system were deposited onto single crystal and sintered polycrystalline Al2O 3 substrates at room temperature and 700°C and subjected to annealing for various periods of time at 700-1000°C. TEM characterization showed that the morphology of the film varied with changes in deposition temperature: a columnar structure was produced at room temperature and layers containing crystalline grains were produced at 700°C. The interfacial structures of the films remained unchanged below 700°C. Interfacial reactions were observed following annealing at 850°C for 5 hours. The phase transformation at the interface was characterized for the film annealed at 1000°C for 5 hours, for which the principal phases were identified as SrAl2-xFe xO4 and SrFe12-yAlyO19. As a result, an isothermal section at 1000°C of a ternary phase diagram for SrO-Al2O3-Fe2O3 is proposed. Evaluation for thin film conductometric sensing applications indicated that the untreated films deposited at 700°C onto both single crystal and sintered Al2O3 substrates exhibited a similar temperature dependency of conductivity in air and a p-type gas sensor response to oxygen and propane at 500°C.

A series of experiments was carried out to compare the structural and electronic properties of intrinsic nanocrystalline silicon (nc-Si:H) thin films deposited via continuous wave (cw) and pulsed (p)-PECVD at 150°C substrate temperature. Working at this temperature allows for the easy transfer of film recipes from glass to plastic substrates in the future. During the p-PECVD process the pulsing frequency was varied from 0.2 to 50 kHz at 50% duty cycle. Approximately 15% drop in the deposition rate was observed for the samples fabricated in p-PECVD compared to cw-PECVD. The optimum crystallinity and photo (σph) and dark conductivity (σD) were observed at 5 kHz pulsing frequency, with ~10% rise in crystallinity and about twofold rise in the σph and σD compared to cw-PECVD. However, for both the cw and p-PECVD nc-Si:H films, the observed σph and σD were one to two orders and three orders of magnitude higher respectively than those reported in literature. The average activation energy (EA) of 0.16 ∓ 0.01 eV for nc-Si:H films deposited using p-PECVD confirmed the presence of impurities, which led to the observation of the unusually high conductivity values. It was considered that the films were contaminated by the impurity atoms after they were exposed to air. Following the thin film characterization procedure, the optimized nc-Si:H film recipes, from cw and p-PECVD, were used to fabricate the absorber layer of thin film solar cells. The cells were then characterized for J-V and External Quantum Efficiency (EQE) parameters. The cell active layer fabricated from p-PECVD demonstrated higher power conversion efficiency (η) and a maximum EQE of 1.7 ∓ 0.06 % and 54.3% respectively, compared to 1.00 ∓ 0.04 % and 48.6% respectively for cw-PECVD. However, the observed η and EQE of both the cells were lower than a reported nc-Si:H cell fabricated via p-PECVD with similar absorber layer thickness. This was due to the poor Short-circuit Current Density (Jsc), Open-circuit Voltage (Voc), and Fill Factor (FF) of the cw and p-PECVD cells respectively, compared to the reported cell. The low Jsc resulted from the poor photocarrier collection at longer and shorter wavelengths and high series resistance (Rseries). On the other hand, the low Voc stemmed from the low shunt resistance (Rsh). It was inferred that the decrease in the Rsh occurred due to the inadequate electrical isolation of the individual cells and the contact between the n – layer and the front TCO contact at the edge of the p-i-n deposition area. Additionally, the net effect of the high Rseries and the low Rsh led to a decrease in the FF of the cells.

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The field of organic electronics has become an increasingly important field of research in recent years. Organic based semiconductors have the potential for creating inexpensive, solution processed devices on flexible substrates. Some of the applications of organic semiconductors include organic field effect transistors, organic light emitting diodes and organic photovoltaics. Functionalized pentacenes have been proven to be viable donor materials for use in organic photovoltaic devices. The goal of this research is to synthesize and test the viability of novel electron deficient pentacenes and pentacene based materials as acceptors to be used as drop-in replacements for PCBM in bulk-heterojunction organic solar cells. Our goal was to tune and improve the efficiencies of these solar cells in a two pronged approach. First we tuned the open circuit voltage of these devices by determining the optimal energy levels of these acceptors by varying the number of electron withdrawing substituents on the acene core. We also tuned the short circuit current by chemically altering the solid state packing and optimizing device processing conditions. A preliminary structure-property relationship of these small molecule acceptors and photovoltaic device efficiency was established as a result.

This dissertation mainly addresses the synthesis of well-ordered mesoporous titania thin films by dip coating with PEO-PPO-PEO triblock copolymer surfactant template P123. Because P123 is composed of poly(ethylene oxide) [PEO] and poly(propylene oxide) [PPO] blocks, concentrations of ingredients are adjusted to tune the films’ wall thickness, pore size and mesophase. Structural changes are consistent with partitioning of species among PEO blocks, PPO blocks, and the PEO/PPO interface. Titanates localize near PEO and increase wall thickness (by 5 nm to 7 nm). Depending on aging temperature, PPG either swells the PPO cores (when it is hydrophobic) or introduces large (>200 nm) voids (when it is hydrophilic but phase separates during heating). 1-butanol localizes at the PEO/PPO interface to favor a 3D hexagonal mesostructure. In another approach, anodizing Ti foils yields vertically aligned titania nanotubes arrays with exceptional stabilities as anodes in lithium ion batteries; they maintain capacities of 130-230 mAhg-1 over 200 cycles. No microstructural changes are induced by battery cycling and good electrical contact is maintained. A diffusion induced stress model suggests that thin-walled nanotubes arrays should be stable under testing conditions, and that ordered hexagonal columnar pore arrays should have both high charge/discharge rates and low stress development.

Stable organic semiconductors are critical to produce inexpensive, efficient and flexible thin film organic solar cells. A current chemical focus is the synthesis of stable, electron-accepting materials to be utilized as an acceptor layer in photovoltaics.1 The Anthony group has shown that the functionalization of pentacene with suitable electron withdrawing groups provides a catalog of suitable acceptors for this purpose.2 These pentacenes can be further modified to pack in a unique 1-dimensional "sandwich herringbone" crystal packing, leading to improved device current.3 To improve the stability of acene acceptors, we have taken two hetero-atom themed approaches. First, we have studied the acenequinone as an electron-accepting chromophore.4 Further, we replaced the terminal aromatic rings with heterocycles, such as furan or thiophene. In order to enhance the crystal engineering versatility of the chromophore, we utilize c-fused heterocycles (rather than the more commonly used b-fused cycles seen in e.g. anthradithiophenes). The c-fused acenequinones can be tetra-functionalized with silylethynyl groups to influence crystal packing and increase solubility.5 The silylethyne groups are known to increase the photostability and lower the energy gap (Eg) of pentacenes.5 The functionalization of the silylethyne groups also aids in lowering the lowest unoccupied orbital (LUMO) of acene structures.5